Black Widow pulsar

The Black Widow pulsar (PSR B1957+20) is an eclipsing binary millisecond pulsar in the Milky Way. Discovered in 1988, it is located roughly 6,500 light-years (2,000 parsecs) away from Earth. It orbits with a brown dwarf or super-Jupiter companion with a period of 9.2 hours with an eclipse duration of approximately 20 minutes. When it was discovered, it was the first such pulsar known.^[7]

Black Widow pulsar

The blue and green are optical images of the field in which the Black Widow pulsar is found, the green indicating the H-alpha bow shock. The red and white are the colors of the shock structures discovered in x-ray by the Chandra X-ray Observatory.
Observation data Epoch J2000      Equinox J2000
Constellation	Sagitta[1]
Right ascension	19h 59m 36.764s[2]
Declination	+20° 48′ 14.90″[2]
Apparent magnitude (V)	20.16 – 26.2[3]
Astrometry
Proper motion (μ)	RA: −19.267 mas/yr[2] Dec.: −26.560 mas/yr[2]
Parallax (π)	1.1878±1.3556 mas[2]
Details
pulsar
Mass	2.4[4] M☉
Rotation	1.607 ms[5]
companion
Mass	0.035[4] M☉
Other designations
QX Sge, PSR J1959+2048, PSR B1957+20[6]
Database references
SIMBAD	data

Description

The prevailing theoretical explanation for the system implied that the companion is being destroyed by the strong powerful outflows, or winds, of high-energy particles caused by the neutron star; thus, the sobriquet black widow was applied to the object. Subsequent to this, other objects with similar features have been discovered, and the name has been applied to the class of millisecond pulsars with an ablating companion, as of February 2023 around 41 black widows are known to exist.^[8][9]

A visual band light curve for QX Sagittae, adapted from van Paradijs et al. (1988)^[10] The light from a nearby star of similar brightness is included, and at the curve's minimum all light comes from that star.

Later observations of the object showed a bow shock in H-alpha and a smaller-in-extent shock seen in X-rays (as observed by the Chandra X-ray Observatory), indicating a forward velocity of approximately a million kilometers per hour.^[11]

In 2010, it was estimated that the neutron star's mass was at least ${\displaystyle 1.66M_{\odot }}$ and possibly as high as ${\displaystyle 2.4M_{\odot }}$ (the latter of which, if true, would surpass PSR J0740+6620 for the title of most massive neutron star yet detected and place it within range of the Tolman–Oppenheimer–Volkoff limit).^[12] In January 2023 the upper limit was revised down to ${\displaystyle 1.8M_{\odot }}$^[13][14]

Planets

The pulsar has a substellar companion, possibly a brown dwarf.

The Black Widow pulsar planetary system^[15]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	22 MJ	—	0.38	—	—	—

Gallery

Artist impressions of the Black Widow pulsar.

• 
  Artist's impression of the pulsar surrounded by its bow shock. White rays indicate particles of matter and antimatter being spewed from the star. Its companion star is too close to the pulsar to be visible at this scale.
• 
  Depiction of the same pulsar one million times closer showing the effect of its wind on its companion star, which is evaporating. The bow shock is too large to be shown, and at this scale would extend more than 15 miles (24 km) beyond the edge of the computer screen.

See also

• PSR J1544+4937
• PSR J1719−1438